1. Field of the Invention
The invention relates to a high pressure discharge lamp. The invention relates especially to a high pressure discharge lamp which is used for an ultraviolet curing device or the like.
2. Description of Related Art
Conventionally, for a light source of a UV curing device in which resin and ink are cured by UV radiation, a high pressure discharge lamp is used. This high pressure discharge lamp is used, for example, also for a device in which coating material which is applied to optical fibers is cured. Such a curing device is disclosed, for example, in Japanese patent disclosure document HEI 2-111475, Japanese patent disclosure document SHO 62-229202, and Japanese patent disclosure document HEI 6-144885.
One such device for curing of coating material which is applied to optical fibers allows the optical fibers to run up and down. For this reason, therefore, a high pressure discharge lamp with a great length is used. The high pressure discharge lamp is located parallel to the optical fibers. To achieve high working efficiency, several such devices are used which are arranged on top of one another in the direction in which the optical fibers run (specifically up and down).
However, due to the height limitation in the plant or for other reasons these devices cannot always be easily placed on top on one another more than once. Therefore, the number of devices and also the number of light sources used cannot be increased at will. Accordingly, in the light sources used for these devices, i.e. in the high pressure discharge lamps, there is a demand for shortening of the entire length of the discharge tube without changing the length between the electrodes.
A device for curing a coating material applied to optical fibers was described above by way of example. However, not only in this device, but also for other purposes, is there a need to shorten the total length of the discharge lamp without changing the length between the electrodes. This means that there is a need for a lamp in which the length "total length of the discharge lamp relative to the length between the electrodes" is shortened as much as possible.
Japanese patent disclosure document HEI 5-82093 discloses a U-shaped discharge lamp in which the discharge part is bent. Here, it is a sodium discharge lamp which is used for interior illumination or similar purposes, a reduction in the size of the overall lamp being desired. It is, therefore, not a lamp with a great length between the electrodes.